A sensor of this general type is known from U.S. Pat. No. 4,007,435.
The known gas sensor has a first supporting substrate to which a heating device is applied, and a second supporting substrate on which various sensor elements are disposed. Both the heating device and the sensor elements are provided with suitable contacts and conductor leads as electrical connections. For operation, both substrates are placed in close contact with one another, so that the lower substrate having the heating device heats the substrate located thereabove, having the sensor elements, to the operating temperature required for the measurement. Since the sensor elements are used for detecting gas components, for instance in automobile exhaust, their surfaces must be exposed freely to the gas flow, and so no other arrangement of the substrate is possible. If the known gas sensor were expanded by using further sensor elements, the second supporting substrate would be enlarged further, which would result in a corresponding enlargement of the first supporting substrate having the heating device.
Because of the large surface area in the layer-like configuration of the known gas sensor, relatively high heating capacities are needed to heat the sensor elements to their operating temperature or to keep them at that temperature, once the latter is attained.
Furthermore, with the known arrangement it is not possible to dispose heat-tone sensors (pellistors), for example, on the second substrate that carries the sensor elements, because the relatively large mass of the supporting substrate means that the temperature changes, which in such cases are only slight, can no longer be detected because of heat dissipation.